(In reply to Boris Zbarsky [:bzbarsky, bz on IRC] from comment #4)
Otherwise, we'll likely do a feature test and fall back to offsetHeight for tables in Firefox.
Wait, why do you need this? Are you trying to determine geometry (in which case getBoundingClientRect might work better), or actual styles?
Good question. In this case it's about styles as we need it for https://api.jquery.com/outerHeight/.
As I understand it, the issue arises from the fact that table is higher than its set CSS height when it contains caption, regardless of box-sizing used. In a way, caption acts like another form of padding or border which affects the table box model.
The problem is that jQuery's outerHeight is supposed to contain all those paddings/borders and return the enclosed element height but it doesn't happen in the case of table due to special caption behavior. In case of padding or border we have box-sizing, though, and there's no analogous way to include caption in height computations.
Due to all that, it may make sense to actually settle on Firefox behavior & document it. But for us it's more important to have consistent behavior in supported browsers. And since there's no spec for that yet, it's hard to make a concrete decision.